The aero-engine casing is a key component for carrying loads. With the purpose of improving the thrust-weight ratio of the aero-engine, the casing is required to be designed to be as thin as possible. Therefore, the vibration of aero-engine's rotor, support, and casing will be easily coupled causing the whole engine's vibration to be more serious. Considering the structural vibration propagation is essentially the vibration energy transmission, the structural intensity (SI) method is popular and widely used to investigate the transmission phenomena of vibration energy in vibrating structures. This method combines forces with velocities to quantify the vibrational energy flow (VEF) transmitted in the structures by its directions and magnitude. Therefore, the SI fields are quantified by the developed computation system which combines the finite element design language and the in-house code. And a model of dual-rotor–support–casing coupling system subjected to the unbalanced forces of the rotors is established in this paper. The scalar and vector diagrams of instantaneous SI fields are visualized to show the main vibration energy transmission paths among these three parts. Moreover, the relationship between the SI and the mechanical energy is derived from the kinetic equation. According to this relationship, the phenomenon that the vibration energy and the strain energy are always converted to each other in the middle part of the rotor shaft with the first-order bending mode is discussed, which reveals the cause of the first-order bending mode of the rotor from a microscopic point of view.

The main goal of the study is to apply the structural intensity method to analyze the effects of positions of the main-mount and the sub-mount on the vibrational energy flow transmission characteristics in aero-engine casing structures, so as to attenuate the vibration of the casing and the whole aero-engine. Structural intensity method, indicating magnitude and direction of the vibrational energy flow, is a powerful tool to study vibration problems from the perspective of energy. In this paper, a casing-support-rotor coupling model subjected to the rotor unbalanced forces is established by the finite element method. Formulations of the structural intensity of a shell element and the structural intensity streamline are given. A simulation system consisting of the finite element tool and the in-house program is developed to carry out forced vibration analysis and structural intensity calculation. The structural intensity field of the casing is visualized in the forms of vector diagram and streamline representation. The vibrational energy flow behaviors of the casing at the rotor design rotating speed are analyzed, and the vibrational energy flow transmission characteristics of the casing with different axial positions of the main-mount and the sub-mount are investigated. Moreover, some measures to attenuate the vibration of the casing are obtained from the numerical results, and their effectiveness is verified in the frequency domain and the time domain. The results shed new light on the effects of the mount positions on the vibration energy transmission behaviors of the casing structure. The structural intensity method is a more advanced tool for solving vibration problems in engineering. Furthermore, it may provide some guidance for the vibration attenuation of the casing and the whole aero-engine.

Vibration control is a permanent and significant issue in all forms of structural dynamic analysis with the consistent objective being to minimize vibration levels. Considering that the propagation of vibration waves is essentially the transmission of vibrational energy flow (VEF), the fundamental requirement, therefore, is to minimize the VEF transmitted from sources to sinks and then to control and block the flow of vibration energy. Structural intensity (SI) method, combining forces with velocities to assess the magnitude and directions of VEF, is alternative to classical dynamic assessment methods offering insight into the transmission of VEF and studying additional phenomena which cannot be obtained by conventional dynamic analysis. In the field of noise, active noise control has been widely used in vehicles and headphones, which has achieved remarkable results by introducing a cancelling ‘anti-noise’ wave through an appropriate array of secondary sources. Analogically, it is considered whether the vibration of the structure can be attenuated by introducing a secondary reverse excitation (SRE) to offset the VEF transmitted in the structure. Therefore, this article combines the SI method and SRE to carry out related research on this issue. The rectangular plate with the circular hole subjected to the transient sinusoidal force, being widely used and found in various engineering branches, is taken as the research object. The developed simulation system consisting of the finite element tool and the in-house program is used to assess and visualize the instantaneous SI fields. The effects of the SRE acting on this structure on the transmission behaviours of VEF and the vibration suppression have been investigated in detail. Moreover, the transmission, conversion and balance relationships of the VEF have been derived from the general equation of motion and analysed as well. This study sheds new light on the vibration attenuation by introducing the secondary source from the perspective of VEF.

Premature seal failure induced by the unevenness of interstage pressure distribution in multi-stage brush seals significantly compromises the sealing efficiency of Air-Turbo Rocket (ATR) engines operating under high-pressure (megapascal-level) differential conditions. Conventional pressure equalization designs for such seals often result in significant leakage rate increases. This study addresses the pressure imbalance phenomenon in four-tooth three-stage brush composite seals through a novel fractal–geometric porous-media model, rigorously validated against experimental data. Systematic investigations were conducted to elucidate the effects of structural parameters and operational conditions on both sealing performance and pressure distribution characteristics. Key findings reveal that, under the prototype structure parameter, the first-, second-, and third-stage brush bundles account for 18.3%, 30.0%, and 43.3% of the total pressure drop, respectively, with grate teeth contributing 8.4%, demonstrating an inherent pressure imbalance. Axial brush spacing exhibits a minimal impact on the pressure distribution, while the gradient thickness settings of the brush bundles show limited influence. Radial clearance optimization and gradient backplate height adjustment effectively regulate pressure distribution, albeit with associated leakage rate increases. Structural modifications based on these principles achieved only a 5.8% leakage increment while reducing the maximum bundle pressure drop by 23%, demonstrating effective pressure balancing. A simplified analysis of entropy reveals that the fundamental mechanism governing the pressure imbalance stems from non-uniform entropy generation caused by aerodynamic damping dissipation across sequential brush stages. These findings establish a dampened dissipation-based theoretical framework for designing high-performance multistage brush seals in aerospace applications, providing critical insights for achieving an optimal balance between leakage control and pressure equalization in extreme-pressure environments.

In order to solve the problem of rotor-rotor inter-shaft labyrinth seal rubbing fault during the test run of a counter-rotating dual-rotor aero-engine, based on the FFT, the vibration time-domain signals of measuring points on the casing are analyzed in the frequency-domain, and the waterfall diagrams of each cross-section measuring point and the spectrum diagrams of the step section of the time-domain signal are drawn. The analysis results show that when the high and low-pressure speeds are both in steady-state, the rotor-rotor inter-shaft labyrinth seal rubbing causes a sudden increase in the amplitude of some measuring points; the spectrum diagrams at the measuring points of the intake casing and turbine casing sections show regular combined frequencies f₁+k₂f₂ and k₁f₁+f₂ characteristics, and the frequency 2f₁+f₂ component is dominant. Finally, based on the vibration TPA method, the vibration characteristics of the rotor-rotor inter-shaft labyrinth seal rubbing fault is analyzed mechanistically, and combined with the results of engine disassembly inspection, it is comprehensively judged that the fault is due to the increase in rotor vibration caused by the rise in high and low-pressure speeds. Furthermore, the labyrinth seal expands more due to the high-temperature than the wear-resistant, resulting in a reduction in the gap between the labyrinth and the wear-resistant coating on the inner side of the high-pressure rotor, which leads to the rotor-rotor inter-shaft labyrinth seal rubbing fault.